The present invention relates to a method for fabricating a semiconductor device and an exposure mask, more specifically, a method for fabricating a semiconductor device which suppresses pattern deformations due to optical proximity effect, and an exposure mask used in the method for fabricating the semiconductor device.
The downsizing of semiconductor devices is realized by shortening the light source wavelength of the exposure systems used in photolithography. Presently, as the light source, argon fluoride (ArF) excimer lasers having wavelength of 0.193 μm have come to be used, and the rule of semiconductor devices has reached the level of not more than 0.1 μm, which is shorter than said wavelength.
In transferring patterns thus exceeding the resolution limit of the exposure wavelength onto a substrate, the positions and the shapes of the ends of the patterns formed on the substrate are changed, and differences are generated between the dimensions of the mask patterns and the dimensions of the patterns transferred on the substrate.
For example, when patterns are transferred onto a substrate with an exposure mask having the patterns 102, 104 as shown in FIG. 23A, the resolution limit takes place at the ends of the patterns, and the transferred patterns 102′, 107′ have the ends shortened as shown in FIG. 23B. This phenomenon is called shortening. The shortening takes place more conspicuously as the pattern width is smaller.
Then, various methods for suppressing such optical proximity effect have been proposed. As one of them, the method for correcting the optical proximity effect called OPC (Optical Proximity Correction) is disclosed in, e.g., Reference 1 (Japanese published unexamined patent application No. Hei 10-289861), Reference 2 (Japanese published unexamined patent application No. 2001-356465) and Reference 3 (Japanese published unexamined patent application No. 2002-250999), etc. The OPC is a method for correcting shapes and dimensions of patterns transferred on a substrate by locally widening mask patterns in advance or laying out dummy patterns in directions opposite to directions of deformations of patterns taking place when the mask patterns are transferred onto the substrate.
Specifically, patterns called hummer heads, which have assist patterns 102a on both sides of the ends of mask patterns 102 as exemplified in FIG. 24A, or as exemplified in FIG. 24B, assist patterns 102b extending the ends of the mask patterns by the same length are laid out, whereby shape changes of the transferred patterns, such as shortening, etc., can be suppressed.
The other related arts are disclosed in, e.g., Reference 4 (Japanese published unexamined patent application No. Hei 10-092714), etc.
However, when mask patters are proximate to each other at the ends, the assist patterns cannot be allowed to be sufficiently large. This is because with the assist patterns being proximate to each other, the transferred patterns become continuous due to the optical proximity effect at the parts where the assist patterns have been added (see FIG. 24C). Accordingly, the assist patterns cannot sufficiently suppress the shortening.
Usually, interconnections have contacts at the ends, and when the shortening takes place in the interconnection patterns, the overlap of the interconnections over the hole patterns becomes insufficient. Accordingly, the contact between the interconnections and the contact plugs buried in the holes becomes insufficient, and, in the worst case, disconnections often take place.